The present invention relates to bleaching and hygienizing compositions having improved chemical and chemical-physical stability which is maintained during the time even after prolonged storage (shelf stability), even over 6 months.
More specifically the invention relates to compositions to be used for preparing tooth pastes of complex compositions.
The bleaching and hygienizing properties of organic peroxiacids, in particular of aliphatic peroxyphthalimidic acids, such as typically the epsilon-phthalimido peroxyhexanoic acid, known as PAP, are known, see for examples EP 325,289 and EP 325,288. The reactivity of the aliphatic peroxyphthalimidic acids makes their use interesting in various applications, but it is also a technical problem from the point of view of the preparation of formulations having high stability during the time. Indeed said organic peroxyacids react very quickly wherefore it is not possible to prepare complex formulations, such as those of the tooth pastes, stable during the time.
The shelf-stability of the tooth paste formulation is therefore an essential feature for the same.
In tooth pastes one could think to use organic peroxyacids and specifically the phthalimido-peroxyalkanoic acids introduced in many component compositions as chemical agents having bleaching and hygienizing action to improve these properties with respect to the conventional compositions, which are based on the physical-mechanical action of the abrasive compounds contained in the tooth pastes. However it must be noted that organic peroxides must be able to operate under particularly mild conditions and at the same time to maintain their activity during the time even after prolonged storage, without changing the system organoleptic characteristics, as defined below.
As regards tooth pastes it is known the efficacy of the proxyacetic acid for the preparation of formulations having an improved bleaching effect, see for example EP 545,594.
The efficacy of phthalimido-alkanoic and/or cationic peroxyacids for the preparation of tooth systems having a bleaching activity is also known, see for example patent application WO 96/05802. In the case of the phthalimido-peroxyalkanoic acids, which have a remarkable chemical reactivity and bleaching and hygienizing activity, besides favourable toxicological properties, it is difficult to obtain monocomponent formulations for tooth pastes having polyfunctional characteristics. In said patent application, in order to prepare tooth pastes, a bicomponent system formed of two complementary but separated formulations, which are mixed together at the time of the use, is employed. This solution allows to maintain all the properties of the phthalimido-alkanoic peroxyacids but from the practical point of view it represents a limitation since it requires more complex equipments typical of bicomponent systems.
The solution which allows to obtain a monocomponent formulation comprising the phthalimido-alkanoic proxyacids has been described in EP 895,777. In this patent adducts between said peroxyacids and cyclodextrins are used, which allow to improve the stability of the peroxycarboxylic acids without reducing the activity and efficacy thereof.
Tests carried out by the Applicant have shown that with the formulations exemplified for tooth pastes in EP 895,777 tooth pastes having a greater stability in the time are obtained, however it is required that tooth pastes of industrial and commercial interest show a greater stability as regards organoleptic properties, also in the long term. More specifically the stability required to tooth pastes of industrial and commercial interest represents not only the substantial maintenance of the active oxygen titre, the sole characteristic of stability reported in EP 895,777, but also the maintenance of the organoleptic properties such as: colour, taste, homogeneity (uniformity) of the paste for a long time, combined with easiness to flow from the consumer tube and maintenance of this feature for a long period, and of the chemical-physical properties such as: pH, density and viscosity.
The need was felt to have available commercially usable tooth paste compositions having improved stability as above defined.
It has been surprisingly and unexpectedly found by the Applicant that it is possible to further improve said stability by the formulations described hereinafter:
An object of the present invention are tooth pastes comprising:
a) imido-alkanpercarboxylic acids of general formula: 
xe2x80x83wherein A is a group of formula 
n is an integer 0, 1 or 2,
R1 is hydrogen, chlorine, bromine, C1-C20 alkyl,
C2-C20 alkenyl, aryl or alkylaryl,
R2 is hydrogen, chlorine, bromine or a group of formula xe2x80x94SO3M, xe2x80x94CO2M, xe2x80x94CO3M, xe2x80x94OSO3M,
M is hydrogen, an alkaline metal or ammonium ion or the equivalent of an alkaline-earth metal ion and x is C1-C19 alkylene or arylene;
Y is a C3-C19, alkylene, under the form of adducts with cyclodextrins, preferably beta-cyclodextrins,
b) aliphatic carboxylic acids having a solubility in water at room temperature higher than or equal to 5% by weight and containing one or more carboxylic functions.
Aliphatic oxyacids containing one or more xe2x80x94OH functions are the preferred components b). In particular, as an example, lactic acid, citric acid, tartaric acid, etc., can be mentioned. Also various kinds of isomers can be used where possible. For example as for tartaric acid the (L), (D), meso or racemic form can be used.
The component b) amount ranges from 0.05 to 5% by weight, preferably 0.1-1% by weight, of the tooth paste.
Preferably component b) is used encapsulated, f.i. as it is common in the pharmaceutical field.
In component a) the molar ratio between the peroxyacids of the invention and cyclodextrins, PAP-cyclodextrins adduct, is in the range 1:1-1:2.
Among immidoalkanpercarboxylic acids of component a) the phthalimido-peroxycarboxylic acids are preferred, more preferably the epsilon-phthalimido-peroxyhexanoic acid.
Among cyclodextrins we can mention alpha, beta, gamma or delta cyclodextrins, modified alpha, beta, gamma or delta cyclodextrins with acyl, alkyl, hydroxyalkyl groups, generally having from 1 to 10 carbon atoms, preferably from 2 to 6; the mixtures of said cyclodextrins and the mixtures of said cyclodextrins with dextrins or linear oligosaccharides; beta-cyclodextrins are preferably used.
A process for preparing the adducts of peroxyacid and in particular of the epsilon-phthalimido peroxyhexanoic acid with cyclodextrins, in particular beta-cyclodextrins, is described in EP 895,777, herein incorporated by reference.
Tooth pastes contain as well known, among others, the conventional components indicated below, which must however show the characteristic to be chemically compatible with component a). This compatibility (COMPATIBILITY TEST) is experimentally determined by measurements of the adduct thermal stability in the presence of the single conventional component. By thermal stability it is meant the maintenance from the component a) of its titre in active oxygen, i.e. a maximum reduction of said titre of 10% after one week of exposure at the temperature of 450xc2x0 C. As typical conventional components: wetting agents, preservatives, thickeners, dyes, aromas, sweeteners, abrasives and detergents can be mentioned.
It has been found by the Applicant that the above test is satisfied with the typical conventional components of the tooth paste.
Among wetting agents there can be water, glycerine, sorbitol; among preservatives: parabens, imidazolidinylurea; among thickeners: cellulose esters, alginates, silica, carrageen; among dyes those of common food use; among aromas especially the derivatives of mint, carnation, anise, orange, bergamot, eucalyptus, etc.; among sweeteners saccharin and its derivatives, xylitol and mannitol; among abrasives: silica, alumina, dihydrate calcium phosphate; among detergents sodium lauryl sulphate, etc.
Preferred tooth pastes according to the invention are the following: (% by weight):
Aromas can be used as such, preferably they are used comilled. With comilled it is meant a mixture between aroma and an inert specific support, for example silica, carboxymethylcellulose and other cellulose derivatives, obtainable for example by a comilling process.